1. Field of the Invention
The invention relates to a process for time-managing the utilization of data detected in a data flow as well as to the device implementing the process.
2. Discussion of Background
The invention finds a particularly advantageous application for time-managing the displaying of subtitles obtained from digital data detected in a data flow conveyed in particular but not exclusively according to the MPEG 2 System transport standard.
In most cases, a data flow conveyed according to the MPEG 2 System transport standard comprises a temporal reference signal commonly denoted PCR (the abbreviation PCR standing for “Program Clock Reference”). The reference signal PCR makes it possible to establish a timescale for the data contained in the flow. Moreover, the data flow also contains synchronization signals commonly denoted PTS (the abbreviation PTS standing for “Presentation Time Stamp”). A synchronization signal PTS is a signal making it possible to implement an action on some of the data conveyed by the flow. For the data corresponding to a subtitle, it may, for example, involve the action of displaying the subtitle in synchronism with the appearance of an image. The display PTS signal associated with a subtitle is conveyed in the header of the subtitle. Its value gives the instant at which the subtitle is to be displayed.
The subtitles generally consist of coded data. It is therefore necessary to decode them before displaying them. The expression coded data should be understood, for example, to mean compressed data which need to be decompressed before display.
In the case where, for example, the instant at which a subtitle is to be displayed is very close to the instant at which this subtitle is detected in the flow, the displaying of a subtitle may have drawbacks. The expression “very close in time” should be understood to mean that the duration which separates the instant at which the subtitle is detected is of the same order of magnitude or less than the duration required for the decoding of the data which represent the subtitle. Under these conditions, the duration of display of the subtitle may be very short and, in the extreme case, the subtitle may be lost.
Moreover, in other cases, the data flow conveyed according to the MPEG 2 System standard does not contain any subtitles display PTS signal. These cases correspond, for example, to simultaneous subtitling where it is desired that the subtitles be displayed as soon as possible after having been detected and decoded. In these cases, when a short subtitle follows a long subtitle, the duration of display of the long subtitle may be less than the duration of display of the short subtitle. Thus, the possible duration of display ΔST1 is then equal to:ΔST1=ΔT+DST2−DST1, where:                ΔT is the interval of time separating the first subtitle ST1 and the subtitle ST2 which follows the subtitle ST1,        DST1 is the duration of decoding of the subtitle ST1, and        DST2 is the duration of decoding of the subtitle ST2.        
For respectively long and short subtitles ST1 and ST2, the durations DST2 and DST1 are respectively short and long. It follows that the duration of display of the long subtitle ST1 is all the shorter as the subtitle ST2 is a short subtitle and the subtitle ST1 is a long subtitle.